Diagnostic ultrasound techniques and applications of transluminal ultrasound imaging to locate and diagnose pathologic conditions of body tissue or obstructions of body lumens are widely known. The book entitled Intravascular Ultrasound--Techniques, Developments Clinical Perspectives, edited by N. Bom and J. Roelandt (Kluwer Academic Publishers, Rotterdam Post-Graduate School of Cardiology, 1989), incorporated herein by reference, describes the equipment used in transluminal ultrasound imaging and a number of applications of such imaging.
Intraluminal ultrasound imaging is widely used in cardiology where the ultrasound transducer is mounted at the tip of a catheter introduced into the vascular system and advanced through the vessels of the heart to obtain cross-sectional ultrasound images of heart vessels at desired locations. In addition, transesophageal ultrasound imaging has been employed in cardiology to scan the heart and blood vessels adjacent to the esophagus. Most of these systems have transducers mounted on special types of tubing, although smaller transluminal devices employing distensible fluid filled bags for contact with the esophogeal wall have also been developed. See, for example, "Rotating Probe for Transoesopnageal Cross-Sectional Echocardiography" by Bertini, et al, Nucl Med Allied Sci, 1984; 28:115-21, incorporated herein by reference.
A wide variety of miniaturized catheter tip mounted ultrasound transducers have been developed as itemized in the first chapter of the aforementioned Bom book. Of these, the multi-element array ultrasound transducers or the rotating ultrasound element transducers or the rotating mirror ultrasound transducers provide, either through electronic switching or mechanical rotation, the ability to scan a cross section of tissue adjacent to the ultrasound transducer.
The development of transluminal ultrasound transducers to some extent coincided with the recent commercialization of percutaneous transluminal coronary angioplasty (PTCA) balloon catheters and the widespread use of endoscopes for visualizing body lumens and cavities. Endoscopes are typically designed to observe areas within a body passageway or cavity. Ordinarily, the endoscope is provided with a first fiber optic bundle to direct illumination from the proximal to the distal end of the endoscope to provide illumination of the area of interest. An additional fiber optic bundle is included to convey a visual image of the illuminated area to the physician.
Although recent advances have been made in transluminal ultrasound and particularly in transesophogeal cardiac imaging and in coronary ultrasound imaging, a number of problems remain in providing a convenient, practical way to perform transbronchial ultrasonography and in particular in combining transbronchial ultrasonography with bronchoscopy.
The bronchial system is filled with air, and thus in order to perform transbronchial ultrasonography it is necessary to fill the space between the ultrasound transducer and the tissue of interest with an ultrasound coupling medium, preferably a fluid sonolucent coupling medium.